A new credit card rule going into effect Sunday, January 27, 2013, could cost you more when shopping with a credit card at some stores.

Visa and Mastercard have agreed to let merchants add a service charge equal to the cost of processing a credit transaction to the bottom line.

The cost of processing is usually 1.5 to 3%, and merchants are capped at a 4% fee under the agreement.

The rule change was made as part of settling an antitrust suit brought by retailers.

Merchants will still not be allowed to add a surcharge to debit card transactions.

However, few stores seem interested in raising their customer’s costs.

“We have discussed the settlement with many, many merchants, and not a single merchant we have spoken to plans to surcharge,” said Craig Sherman, spokesman for the National Retail Federation, which was not involved in the lawsuit.

Wal-Mart, Target, Sears and Home Depot all told NBC News that they had no plans to add a credit card surcharge.

California, Colorado, Connecticut, Florida, Kansas, Maine, Massachusetts, New York, Oklahoma and Texas all ban credit card surcharges.

Both Visa and MasterCard have rules requiring retailers to handle credit cards the same way in every store regardless of location, so if a chain has a store in a state where surcharges are banned then none of its locations would be allowed to have a surcharge.

Under the settlement terms, a merchant adding surcharges on Visa or MasterCard would have to do the same with American Express cards, but that company prohibits surcharge fees.

“The bottom line is that very few retailers would be able to surcharge under the settlement, and that the vast majority don’t want to surcharge even if they could,” Craig Sherman said.

“In the brick-and-mortar world, no one who does any sort of volume business is going to want to surcharge because it will drive their customer crazy and slow down transactions,” agreed Ed Mierzwinski, Director of Consumer Programs at U.S. PIRG.

With the exception of small retailers, credit surcharges are not a major issue for most businesses.

A new credit card rule going into effect Sunday, January 27, 2013, could cost you more when shopping with a credit card at some stores

Still, over time they could become popular as a way for stores to make extra money.

That’s because stores already factor in the cost of processing a credit care when they price their merchandise. Unless they dropped their prices, second charge would be double-dipping at the loss of the consumer.

“We shouldn’t have gotten to the point, but unfortunately because of the court settlement we have,” said Edgar Dworsky, founder of ConsumerWorld.org.

“There’s no one standing up for consumers and saying that this is really bad.”

He notes that in Australia, where surcharging originated in 2003, extra charges have boomed to the point where one-third of retailers charge extra to use a credit card.

Advocacy group Consumer Action warns shoppers to watch their receipts and argue any fees that don’t belong.

“Customers shouldn’t stand for it,” said Ruth Susswein, Consumer Action’s deputy director of national priorities.

“Our advice is to tell them you don’t like the fee and this makes you want to take your business elsewhere.”

If a retailer plans to add a surcharge they are require to post a notification at the store’s entrance.

The exact surcharge per cent needn’t be disclosed until the sale.

Online stores with a surcharge will not be required to have a notice until shoppers reach the page where credit cards are first mentioned, which is most often the final step of checkout.

“We’re not convinced this is going to be an issue,” Ruth Susswein said.

“They may never do it, but as individual consumers we need to be aware.”